The previous papers of the research group have already found that the excitation of a 1310 nm endogenous pump by signal feedback combined with a single fiber Bragg grating (FBG) under the condition of 1240 nm pumping can significantly enhance the gain effect of bismuth-doped fiber amplifiers (BDFA) at long wavelengths. In order to further clarify the effect of the endogenous pump generation mode and the different feedback mechanisms on the broadening effect, we have used a tunable dual grating combined with a controllable pump/signal feedback amplifier structure, and compare in detail the broadening characteristics under the different conditions mentioned above. The experimental results show that any form of endogenous pumping can result in amplification bandwidth expansion, but there is a difference in the behavior of the broadening due to the dual grating line cavity versus the grating-signal reflector line cavity, as well as in the degree to which the broadening is affected by the pump feedback. The effective utilization of this property can provide positive assistance in enhancing the gain-bandwidth performance of BDFA as well as in improving the transmission capacity of communication systems.
This paper presents a double-pass low-noise bismuth-doped fiber amplifier based on a Sagnac comb filter. The amplifier utilizes a Sagnac loop to filter out spontaneous emission light outside the signal wavelength, effectively decreasing the noise figure. Experimental results show that the amplifier achieves a minimum noise figure of only around 3.7 dB. Moreover, its gain bandwidth can cover a significant portion of the O-band. Under a forward pump power of 0.538 W, with an input signal power of -30 dBm, the amplifier can reach a gain of 29.6 dB, while the noise figure is only approximately 4 dB. Under backward pump, the gain difference for different input signal powers is larger compared to forward pump. We also studied the variation of gain with input signal power at a pump power of 0.5 W, using both forward and backward pump methods. The results indicate that the pump direction has a minor impact on the gain but significantly affects the noise figure, with the noise figure under forward pump being 1-2 dB lower than that under backward pump. Additionally, the amplifier exhibits a maximum saturation output power of approximately 9.5 dBm. In conclusion, this amplifier has great potential for application in WDM communication systems.
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